When you get to the appeals council statistically the chances of winning are much better. Keep the faith.
Admittedly, I had to look up myasthnia gravis. It appears it is a musculoskeletal disorder. These disorders are covered under the SSA'a Blue Book Adult listings 1.00. Here's the link http://www.ssa.gov/disability/profes...etal-Adult.htm
Your disease meets the general requirements. But the listing speaks to joints in the specific listings. So, the SSA can make a medical equivalence decision or your case can continue through the 5-step sequence process of evaluation. http://ssdi-help.com/ssabasicinfo/claim-evaluation.htm
It is critical you collect medical evidence, going back as far as you can remember you had this problem. Evidence that proves the symptoms you had even though you were not diagnosed.
Also, complete the Adult Function Report, http://ssdi-help.com/ssaforms/ssa-forms.htm
Make your answers as detailed as possible for the work environment and your daily life. Also, if you can have a doctor complete the Physical Residual Capacity(same llink as previous), it will go a long way towards getting a positive decision.
The bad news is that the Appeals Council has a heavy backload and it takes about a year before your case is reviewed.The upside is that it gives you a year to collect medical evidence and get the recommended forms completed. But, don't delay getting medical records is a tedious job.
Also, check out county health facillities and cllinics that charge on a sliding fee scale. Have you applied for Medicaid? That willl give you baasic healthcare coverage.
Don't hesitate to contact me if you have any more questions.